Electrical resistance device



Feb. 26, 1929. 1,703,809

C. W. WYMAN ELECTRICAL RESISTANCE DEVICE Filed Dec. 5, 1925 Patented Feb. 26, 1929 UNITED STATES PATENT OFFICE.

CHARLES W. WYMAN, OF CLAREMONT, NEW HAMPSHIRE, ASSIGNOR TO SULLIVAN MACHINERY COMPANY, A CORPORATION OF MASSACHUSETTS.

ELECTRICAL RESISTANCE DEVICE.

Application filed December 3, 1925. Serial No. 72,996.

This invention relates to electrical resistance devices and particularly to electrical resistance devices of a type adapted for use in motor rheostats.

With the increasing difiiculty in obtaining mica, the cost of resistances in which mica is the insulating material is becoming prohibitive and accordingly the provision of an arrangement in which a fire proof insulating material of a much less expensive nature may be used is very desirable. Moreover, it is desirable that the resistance units shall be so arranged that the burning out of any portion will involve the elimination of as small a part of the complete device as possible. It is further desirable that an arrangement be provided in Which the replacement of parts which have been destroyed may be readily accomplished and in which moreover there is adequate provision for the expansion of the resistance material at the high temperature sometimes encountered during periods of overload or the like.

Among the objects of the present invention is the provision of an improved electrical resistance, a further object being to provide a resistance which is of a multi-unit construction and employs materials of comparatively low cost. A still further object of the invention is to provide an improved resistance of the multi-unit type in which the units are held in appropriate relation in a simple manner permitting their ready replacement and in which provision is made for the dissipation of heat and for expansion and contraction of the resistance element. Other objects and advantages of the invention will subsequently appear.

In the accompanying drawings in which for purposes of illustration one form the invention may assume in practice is disclosed:

Fig. 1 is a perspective view, with parts removed, of an assembled resistance.

Fig. 2 is a side elevation of one of the resistance'units which is used in making up a complete resistance.

Fig. 3 is a vertical section on the line 33 of Fig. 2.

Referring to the drawings and particularly to Fig. 2 there will be observed a generally rectangular block 1 of fire proof dielectric material, an appropriate material being an asbestos board, though many other suitable materials will suggest themselves to one skilled in the art. These blocks may be cast or molded or sawed from larger slabs of material. Each of the blocks 1 is provided at its opposite end in the form illustrated with a semi-circular recess 2 for reception of holding means later described and is provided with a flattened helically extending peripheral groove 3 extending substantially from one end of the block to the other. Adjacent the opposite ends of the block there are provided transversely extending openings 4 having inclined walls 5. Upon each block is Wound a fiat strip of metallic resistance metal or ribbon 6 of any suitable material, the ribbon being passed from the upper end at one corner diagonally downward through one of the passages 4 and about the helical recess 3 to the opposite end of the block at which it is extended in the opposite direction through the other recess 4 and brought up in the form of a short upstanding lug. The ribbon is wound with reasonable snugness and ordinarily only partially fills the channels It is here to be observed that adjacent passes of the groove 3 are separated by ribs 7 which at each side of the block lie diagonally transverse to the grooves on the other side.

In practice a number of resistance units of this character are mounted in juxtaposition to each other and have their resistance elements suitably connected together. Referring to Fig. 1 there is shown an assembled resistance of this type. Here it will be observed that a pair of end plates 10 provided with lugs 11 for the reception of holding bolts are arranged facing each other. The lugs 11 are provided with suitable insulating rings 12 at their opposite ends and are traversed longitudinally by bushings 13, also of insulating material. Between each unit 1 and its next adjacent unit is arranged a slab or plate 14 of insulating material which may be of the same kind as the plates 1, the plates 14, however, being slightly higher from top to bottom the more effectually to insulate the adjacent units from each other and having semi-circular recesses 15 corresponding to therecesses 2. If desired, these plates might be omitted since the disposition of the ribs 7 on one block diagonally transverse to the grooves 3 on the next would prevent contact of the resistance elements. The several plates 1 and 14 are clamped together by longitudinally extending rods 16 having nuts 17 thereon and suitably insulated if desired by means of insulating sleeves 18. A number of the sheets 14 are placed at either end of the cornplete resistance adjacent the plates 10 to provide for a more certain insulation andif de-" sired a thin plate or a few sheets of mica may be placed directly against the end members 10. In connecting up the resistance units various schemes may be employed, but a preferred system involves the use of approximately U-shaped clips 19 traversed by set screws 20 and if desired also provided with check or lock nuts 21. WVhen a single series of units is used the open sides of the clips may face the center of the units, but when a plurality of series of units are arranged parallel to each other the clips preferably face outwardly so that in the event of loosening adjacent clips can only move apart. Herein at the left hand side of the adjacent end of the resistance in Fig. 1 a'clip designated 19 for purposes of distinction is shown attached to the free end of the first resistance unit 1. If desired, to stiffen the connection of the contact 19, a second L-shaped piece of resistance material may be disposed opposite the free end of the resistance strip 6, or the latter may be made a little longer than necessary so that its free end may be extended down between the block 1 and the adj acent partition or division plate 14 and then turned back into the opening 4:. The opposite end of the resistance ribbon 6 of the first unit is connected by a clip 19 to the adjacent end of the ribbon 6 of the next adjacent unit,

the latter ribbon extending across the top of the partition plate 14: and both the ribbon ends being gripped in overlapping relation by the set screw 20. Similar methods of connecting the ribbon ends of adjacent units are employed throughout the entire length of the resistance and check or lock nuts 21 may be applied on any or all of the set screws 20 as may be desired, these check or lock nuts 21 also serving for connection of the lead off wires from the resistance units where needed.

From the description so far given it will be apparent that the invention marks a substantial improvement in resistance constructions since, should the ribbon burn out at any point,

by simply taking off the nuts 17, withdrawmg rods 16, and releasing the proper set screws 20 the old unit may be removed and a new one substituted very readily. It will also be evident that as the resistance ribbon 6 heats up it is freeto expand longitudinally of the grooves 3 and moreover since the grooves 3 may be made a little deeper than the thickness of the ribbon it will be evident that the latter may be well protected by radiation and conduction since air can freely circulate through the grooves if desired. It will further be observed that should'any plate 14 be disintegrated the ribs 7 might still prevent short circuiting between adjacent ribbone 6.

lVhile'I have in this application described i one form which my invention may assume in practice, it will be understood that this form of the sam'e'is shown for purposes of illustration and that the invention may be modi lied and embodied in various other forms without departing from its spirit or the scope of the appended claims. v

lVhat 1 claim as new and desire to secure by Letters Patentis 1. A resistance unit comprising, in combination, a plurality of connected resistance elements each comprising a fiat block of insulating material having a continuous helically extending groove formed on the sides thereof, a ribbon conductor wound around said element in said grooves, said grooves being deeper than the thickness of said conductor-and each of said elements having a notch formed in each end thereof, said elements being arranged vertically and side by side, a plate on each end of said assembly arranged adjacent and parallel with each end element,

and tensioning means extending between said plates and engaged in said notches on the resistance elements for pressing said elements together and holding them in assembled relation. I 2. An electrical resistance unit comprising in combination, a series of connected resistance elements, each comprising a rectangularly shaped block of insulating mater al having a hclically extending groove formed in the sides thereof, a conductor wound around said block in said grooves, said elements being ar ranged vertically in sideby side relationship, and means for pressing said elements together whereby they are held in assembled relation. I

8. An electrical resistance unit comprising, in combination, a series of connected resistance elements each comprising a. rectangularly shaped block of insulating material having a continuous helically extending groove formed on the periphery thereof, a conductor wound around said block in said groove, said elements being arranged vertically in side by side relationship so that the grooves on the side of one element incline in the opposite direction to the grooves on the opposing face being materially deeper than the thickness of. specified in claim 2 wherein an insulating said conductor whereby substantially vertical board is inserted between adjacent resistance passages are provided for the circulation of elements and held in assembled relation 10 air between the elements when assembled, and therewith.

5 means for pressing said elements together and In testimony whereof I affix my signature.

holding them in assembled relation.

5. An electrical resistance unit of the type CHARLES W. WYMAN. 

